They sell different shade lenses for standard helmets so the adjustment does the same thing on the auto dark. Mine varies from 8 to 13 with 13 being the darkest. There are general rules for what shade to use for what type welding but everyone I know uses the darkest shade they can and still see what they are welding. I am old and use 8 which is really not so good but what I have to do to see. I have never seen any lighter than 8 myself. RM
I bought a millermatic 135 MIG welder. I also looked on google and found a chart from Lincoln that shows based on what type of welding you do and what amps you are welding at which shade to use. It looks like an 11-12 shade is pretty good, 13 is only needed for really high-amp welding.
10-12 is for Mig welding. 13 is needed if welding aluminum with a Tig.
3-5 is for oxyfuel cutting and welding.
If you are having trouble seeing with the proper shade then use the magnifying inserts. They come in .75- 2.50 magnification and go on the inside of the helmet. I've only found the narrow window type but I tape one inside my large window helmet.